Compelling evidence links dietary sodium intake with the prevalence of hypertension in several human population groups around the world. Epidemiologic studies of man and selective inbreeding studies in rats suggest that most population groups contain individuals who are either salt-sensitive, salt-resistant, or who lie somewhere in between. Limited, short-term human studies suggest that the hemodynamic basis of these differences lies in sodium's property of decreasing vascular resistance in normal subjects while increasing resistance in hypertensive subjects. Additional studies are needed to verify this important point and to determine its long-term significance. Non-invasive methods of estimating changes in total peripheral vascular resistance in response to dietary sodium manipulation using echocardiography and venous occlusion plethysmography will be tested as a means of identifying salt-sensitive individuals in the population who might benefit from preventive dietary measures. These methods have the advantage of avoiding the anxiety-provoked sympathetic nervous system stimulation associated with the placement of right heart catheter or intra-aeterial cannulae. The relative effect of dietary potassium on peripheral vascular resistance will also be studied. The groups to be studied will include normal subjects, normotensive subjects with a family history of hypertension, subjects with labile essential hypertension and subjects with mild, fixed essential hypertension. The relationships of dietary sodium and potassium with urinary prostaglandin excretion in the various groups of patients will also be explored.